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  1.   Trademarks
  2. 1Introduction
  3. 2IEEE Specification and How to Derive the Formula
  4. 3Formula Helper to Calculate Limit
  5. 4Conclusion and Summary
  6. 5References

2 IEEE Specification and How to Derive the Formula

The IEEE 802.3-2018, Subclause 40.6.1.2.1 is written as follows:

    "The absolute value of the peak of the waveform at points A and B, as defined in Figure 40–20, shall fall within the range of 0.67 V to 0.82 V (0.75 V ± 0.83 dB). These measurements are to be made for each pair while operating in test mode 1 and observing the differential signal output at the MDI using transmitter test fixture 1 with no intervening cable. The absolute value of the peak of the waveforms at points A and B shall differ by less than 1% from the average of the absolute values of the peaks of the waveform at points A and B. The absolute value of the peak of the waveform at points C and D as defined in Figure 40–20 shall differ by less than 2% from 0.5 times the average of the absolute values of the peaks of the waveform at points
    A and B."

See Figure 40–20—Example of transmitter test mode 1 waveform (1 cycle) in the IEEE specification for further explanation of the points A and B:

The second paragraph of the specification description in section 40.6.1.2.1 contains the description of the math formula required to calculate “Peak A vs. Peak B”: The absolute value of the peak of the waveforms at point A and B shall differ by less than 1% from the average of the absolute value of the peaks of the waveform at point A and B.

The first part of the sentence “the absolute value of the peak of waveforms at point A and B” means that each of them individual waveforms need to comply to the next part of the sentence. It also means that signs of the measurement values have to be removed and the absolute value must be used.

The second part of the sentence “… average of the peaks of the waveforms at point A and B” refers to the following percentage error formula.

The percentage error formula is defined as follows:

    Percent Error Applied when comparing an experimental quantity, with a theoretical quantity, which is considered the “correct” value. The percent error is the absolute value of the difference divided by the “correct” value times 100.
Equation 1. G e n e r i c   f o r m u l a :   P e r c e n t   e r r o r =   E   - T T × 100 %

E is the measured value, either Peak A or Peak B.

The theoretical quantity T is defined as the average of Va and Vb, which is calculated as:

Equation 2. T = V A + V B 2

When Peak A absolute value is Va and Peak B absolute value is Vb, the following formula of the IEEE specification and the percent error formula can be derived:

Equation 3. p e r c e n t   e r r o r   f o r m u l a   = V B - V A + V B 2 V A + V B 2   × 100 %